Submarine Branching Unit
Encyclopedia
A submarine branching unit is a piece of equipment used in submarine telecommunications cable systems
to allow the cable to split to serve more than one destination. For example, one branch might head for a cable landing point
and others may continue.
There are several methods by which the split can be effected, which can also depend on the type of cable system:
In both types of cable system, more than one technique can be used simultaneously.
The conventional symbol used for a submarine branching unit in maps of cable routes is a small equilateral triangle with (usually) one vertex pointing towards the top of the map.
Submarine communications cable
A submarine communications cable is a cable laid on the sea bed between land-based stations to carry telecommunication signals across stretches of ocean....
to allow the cable to split to serve more than one destination. For example, one branch might head for a cable landing point
Cable landing point
A cable landing point is the location where a submarine or other underwater cable makes landfall. The term is most often used for the landfall points of submarine telecommunications cables and submarine power cables. The landing will either be direct or via a branch from a main cable using a...
and others may continue.
There are several methods by which the split can be effected, which can also depend on the type of cable system:
- Purely electrical systems (now almost obsolete) can be split either:
- by physically separating the signal cables so some go in one direction and some in another. This requires no additional power; or
- by using an add-drop multiplexerAdd-drop multiplexerAn add-drop multiplexer is an important element of an optical fiber network. A multiplexer combines, or multiplexes, several lower-bandwidth streams of data into a single beam of light...
to direct the signals down one path or the other. The electrical equipment that acts as the add-drop multiplexer will need powering.
- Optical fibre cable systems can be split either:
- by physically separating the signal-carrying fibres so some go in one direction and some in another. This requires no additional power; or
- Converting the optically carried signals to electrical signals, using an add-drop multiplexer to divide and recombine the signals on the desired paths, the reconverting back to optically carried signals. This signal conversion and multiplexing equipment will require power; or
- Using optical switches to direct optical carrier frequencies down desired paths. The power requirements of optical multiplexing in this manner will be lower than the previous method.
In both types of cable system, more than one technique can be used simultaneously.
The conventional symbol used for a submarine branching unit in maps of cable routes is a small equilateral triangle with (usually) one vertex pointing towards the top of the map.